Ok none of this may be causing your problem, but you will have to check all your voltages, the VFD if the voltage was to high it would fault so that part should be ok, checking for noise plug in an old TV near you cabinet or machine and see how the screen reacts, you will see the noise on the screen if there is any, this saves buying a meter to check for EMF / EMI
So this leaves the drives and the low voltage to check
The motion card check that you have 24v, this can not be more than the 24v
Then check your drives to see that the voltage in within there spec, usually they can be with in 15% to 20% of spec